1. Field of the Invention
The present invention relates to ignition systems for internal combustion engines. More particularly, the present invention relates to electrical AC ignition systems that are used for the igniting of fuel within the internal combustion chambers of the internal combustion engines. More particularly, the present invention relates to electronic spark timing control of an AC ignition coil which supplies applies an AC voltage for the ignition of the spark plug(s) within the internal combustion engine.
2. Description of Related Art Including Information Disclosed Under 37 CFR 1.97 and 37 CFR 1.98
Most internal combustion engines have some type of an ignition circuit to generate a spark in the cylinder. The spark causes combustion of the fuel in the cylinder to drive the piston and the attached crankshaft. Typically, the engine includes a plurality of permanent magnets mounted on the flywheel of the engine and a charge coil mounted on the engine housing in the vicinity of the flywheel. As the flywheel rotates, the magnets pass the charge coil. A voltage is thereby generated on the charge coil and this voltage is used to charge a high-voltage capacitor. The high-voltage charge on the capacitor is released to the ignition coil by way of a triggering circuit so as to cause a high-voltage, short-duration electrical spark across the gap of the spark plug(s) and ignite the fuel in the cylinder. This type of ignition is called a capacitive discharge ignition.
Typically, the engine control module provides an electronic spark timing pulse which is used to command a given spark event for a given engine cylinder. This electronic spark timing pulse is commanded for a given amount of time to charge the primary coil to the desired current or energy. The electronic spark timing pulse duration is often referred to as “dwell-time” or charging time for a given coil and engine operating condition. For example, during cold starting conditions, when the engine is cold and the battery voltage is low, the electronic spark timing control signal for a given cylinder may have an extended pulse duration to fully charge the coil to generate the necessary energy in the primary coil. The energy is then transferred to the secondary coil that is connected to the spark plug output. Similarly, during hot engine conditions and nominal battery voltage, the electronic spark timing pulse can be commanded to have a shorter duration to fully charge the primary coil to a given energy level. As a result, a given electronic spark timing pulse for commanding a given DC coil operation will vary the dwell time or charging time depending on several engine sensor inputs and desired engine operating conditions.
Current DC ignition systems use the electronic spark timing pulse to command a semiconductor power switch device which is connected to the primary coil and allows the coil to reach a targeted primary current or energy. When the semiconductor power device is switched off, the stored energy in the primary coil is then transferred to the secondary coil and available voltage of approximately 40,000 volts can be provided to the spark plug output based on the clamping voltage of the power semiconductor switch and the turns ratio of the secondary-to-primary windings.
Therefore, the high-voltage spark is commanded by the falling edge of an electronic spark timing pulse. This translates to a command “turn-off” of the semiconductor power device. Energy is then transferred to the spark plug with an exponential voltage decay. Typically, one spark event occurs for each electronic spark timing cycle for a given engine cylinder. This method of control has been employed by numerous engine control module designs using command DC ignition systems for many years and has become the general method of firing a given spark plug used in internal combustion engines.
The design of standard reciprocating internal combustion engines which use spark plugs and DC induction coils to initiate combustion have, for years, utilized combustion chamber shapes and spark plug placements which are heavily influenced by the need to reliably initiate combustion using a single short-duration spark of relatively low energy intensity that is timed to fire off the falling edge of the given electronic spark timing pulse.
In recent years, however, increased emphasis has been placed on fuel efficiency, completeness of combustion, exhaust cleanliness, and reduced variability in cycle-to-cycle combustion. This emphasis has meant that the shape of the combustion chamber must be modified and the ratio of the air-fuel mixture changed. In some cases, a procedure has been used which deliberately introduces strong turbulence or rotary flow to the air-fuel mixture at the area where the spark plug electrodes are placed. This often causes an interruption or blowing out of the arc. This places increasing demands on the effectiveness of the combustion ignition initiation process.
In the past, various patents have issued with respect to such ignition systems. For example, U.S. Pat. No. 5,806,504, issued on Sep. 15, 1998 to French et al., teaches an ignition circuit for an internal combustion engine in which the ignition circuit includes a transformer having a secondary winding for generating a spark and having first and second primary windings. A capacitor is connected to the first primary winding to provide a high-energy capacitive discharge voltage to the transformer. A voltage regulator is connected to the secondary primary winding for generating an alternating current voltage. A control circuit is connected to the capacitor and to the voltage generator for providing control signals to discharge the high-energy capacitive discharge voltage to the first primary winding and for providing control signals to the voltage generator so as to generate an alternating current and voltage.
U.S. Pat. No. 4,998,526, issued on Mar. 12, 1991 to K. P. Gokhae, teaches an alternating current ignition system. The system applies alternating current to the electrodes of a spark plug to maintain an arc at the electrodes for a desired period of time. The amplitude of the arc current can be varied. The alternating current is developed by a DC-to-AC inverter that includes a transformer that has a center-primary and a secondary that is connected to the spark plug. An arc is initiated at the spark plug by discharging a capacitor to one of the winding portions at the center-primary. Alternatively, the energy stored in an inductor may be supplied to a primary winding portion to initiate an arc. The ignition system is powered by a controlled current source that receives input power from a source of direct voltage, such as a battery on the motor vehicle.
In each of these prior art patents, the devices used dual mechanisms in which high-energy discharges were supplemented with a low-energy extending mechanism. The method of extending the arc, however, presents problems to the end-user. First, the mechanism is, by nature, electronically complex in that multiple control mechanisms must be present either in the form of two separate arc mechanisms. Secondly, no method is presented for automatically sustaining the arc under a condition of repeated interruptions. Additionally, these mechanisms do not necessarily provide for a single functional-block unit of low mass and small size which contains all of the necessary functions within.
U.S. Pat. No. 6,135,099, issued on Oct. 24, 2000 to T. Marrs, discloses an ignition system for an internal combustion engine that comprises a transformer means having a primary winding adapted to be connected to a power supply and having a secondary winding adapted be connected to a spark plug. The transformer serves to produce an output from the secondary winding having a frequency of between 1 kHz and 100 kHz and a voltage of at least 20 kV. A controller is connected to the transformer so as to activate and deactivate the output of the transformer means relative to the combustion cycle. The transformer serves to produce the output having an alternating current with a high-voltage sine wave reaching at least 20 kV. A voltage regulator is connected to the power supply into the transformer so as to provide a constant DC voltage input to the transformer. The transformer produces power of constant wattage from the output of the secondary winding during the activation by the controller. The controller is connected to the transformer so as to allow the transformer to produce an arc of controllable duration across the electrode of the spark plug. This duration can be between 0.25 milliseconds and 4 milliseconds. A battery is connected the primary winding of the transformer. The battery produces a variable voltage of between five and fifteen volts.
It is object of the present invention to provide an electronic spark timing control system that produces a spark arc of a controllable duration.
It is another object of the present invention to provide an electronic spark timing control system that allows various spark arc patterns across the electrode of the spark plug(s).
It is another object of the present invention to provide electronic spark timing control system that promotes fuel efficiency.
It is another object of the present invention provide electronic spark timing control system which provides complete combustion and exhaust cleanliness.
It is another object of the present invention to provide electronic spark timing control system that reduces variability in cycle-to-cycle combustion.
It is another object of the present invention to provide an electronic spark timing control system that provides the ability to pulse the spark arc.
It is still another object of the present invention to provide electronic spark timing control system that allows for a very small AC ignition coil to be used.
These and other objects and advantages of the present invention will become apparent from a reading of the attached specification and appended claims.